Formation Of Ketene Research Articles

Molecular Understanding of the Catalytic Consequence of Ketene Intermediates under Confinement.

Neutral ketene is a crucial intermediate during zeolite carbonylation reactions. In this work, the roles of ketene and its derivates (viz., acylium ion and surface acetyl) associated with direct C–C bond coupling during the carbonylation reaction have been theoretically investigated under realistic reaction conditions and further validated by synchrotron radiation X-ray diffraction (SR-XRD) and Fourier transformed infrared (FT-IR) studies. It has been demonstrated that the zeolite confinement effect has significant influence on the formation, stability, and further transformation of ketene. Thus, the evolution and the role of reactive and inhibitive intermediates depend strongly on the framework structure and pore architecture of the zeolite catalysts. Inside side pockets of mordenite (MOR), rapid protonation of ketene occurs to form a metastable acylium ion exclusively, which is favorable toward methyl acetate (MA) and acetic acid (AcOH) formation. By contrast, in 12MR channels of MOR, a relatively longer lifetime was observed for ketene, which tends to accelerate deactivation of zeolite due to coke formation by the dimerization of ketene and further dissociation to diene and alkyne. Thus, we resolve, for the first time, a long-standing debate regarding the genuine role of ketene in zeolite catalysis. It is a paradigm to demonstrate the confinement effect on the formation, fate, and catalytic consequence of the active intermediates in zeolite catalysis.

Acetic acid conversion to ketene on Cu2O(1 0 0): Reaction mechanism deduced from experimental observations and theoretical computations

Ketene, a versatile reagent in production of fine and specialty chemicals, is produced from acetic acid. We investigate the synthesis of ketene from acetic acid over the (3,0;1,1) surface of Cu2O(100) through analysis of the adsorption and desorption characteristics of formic and acetic acids. The results allow us to establish a reaction mechanism for ketene formation. Observations from x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy, and temperature programmed desorption (TPD), supported by a comparison with formic acid results, suggest that acetic acid reacts with Cu2O through deprotonation to form acetate species coordinated to copper sites and hydroxylation of nearby surface oxygen sites. For formic acid the decomposition of adsorbed formate species results in desorption of CO2 and CO while, for acetic acid, high yields of ketene are observed at temperature >500 K. Modeling by density functional theory (DFT) confirms the strong interaction of acetic acid with the (3,0;1,1) surface and the spontaneous dissociation into adsorbed acetate and hydrogen atom species, the latter forming an OH-group. In an identified reaction intermediate ketene binds via all C and O atoms to Cu surface sites, in agreement with interpretations from XPS. In the vicinity of the adsorbate the surface experiences a local reorganization into a c(2 × 2) reconstruction. The total computed energy barrier for ketene formation is 1.81 eV in good agreement with the 1.74 eV obtained from TPD analysis. Our experimental observations and mechanistic DFT studies suggests that Cu2O can operate as an efficient catalyst for the green generation of ketene from acetic acid.

Synthesis of the C1−C16 Polyol‐Containing Macrolactone of 13‐Desmethyl Lyngbouilloside, an Unnatural Analog of the Originally Assigned Structure of (−)‐Lyngbouilloside

AbstractThe synthesis of the C1−C16 polyol‐containing macrolactone of 13‐desmethyl lyngbouilloside, an unnatural analog of the originally assigned structure of (−)‐lyngbouilloside is reported. Synthesis of the C1−C16 acyclic backbone is achieved via iterative use of a phosphate tether‐mediated one‐pot sequential, RCM/CM/chemoselective diimide reduction, with concomitant use of a regio‐ and diastereoselective cuprate addition using Me2Zn/CuCN ⋅ 2LiCl or Pd‐catalyzed reductive allylic transposition, respectively on bicyclo[4.3.1]phosphate‐containing subunits. Subsequent oxidative cleavage and Roskamp homologation completes the pathway to the C1−C16 acyclic fragment. Two routes to the macrocyclic core were explored with mixed success, (i) a Boeckman‐type acylketene trapping of the C13 secondary carbinol and (ii) an alternative route employing acid‐catalyzed pyran‐mixed ketal formation via reaction of the C7 secondary carbinol with the β‐keto ester using trimethylorthoformate, and subsequent Yamaguchi cyclization.

Anharmonic Vibrational Frequencies and Spectroscopic Constants for the Detection of Ethynol in Space

The ethynol (HCCOH) molecule has recently been shown to be present in simulated astrochemical ices possibly linking it to molecular building blocks for interstellar complex organic molecules like amino acids. The proposed reaction mechanism suggests the simultaneous formation of both ketene and ethynol from mixed carbon monoxide/water ice in simulated interstellar conditions. Rigorous anharmonic spectral data within both the IR and microwave regions are needed for possible detection of ethynol in the interstellar medium. This study provides the first such data for this molecule from high-level quantum chemical computations where experiment is currently lacking. Ethynol has aBeffcomparable to, but distinct from acetonitrile at 9,652.1 MHz and three notable infrared features with two in the hydride stretching-regions and the C–C stretch at 2,212.8 cm−1. The ketene isomer has already been detected in the interstellar medium, and the possible detection of ethynol made possible by this work may lead to a deeper understanding of the proposed ice formation mechanism involving both species and how this relates to the molecular origins of life.

In(III)‐Catalyzed O‐Annulation of Cyclic Diazodicarbonyls with 2‐Naphthol, 6‐Quinolinol, β‐Tetralone, and 9‐Phenanthrol to Access Diverse Benzochromones

In(III)‐Catalyzed O‐annulation of cyclic diazodicarbonyl compounds with 2‐naphthols, 6‐quinolinol, β‐tetralone, and 9‐phenanthrol is developed. This novel synthetic strategy paves a facile and desired access to diverse and functionalized benzochromones. This imperative protocol involves domino carbene generation, ketene formation through Wolff‐rearrangement, nucleophilic addition, H‐migration, intramolecular cyclization, and elimination of water.

Long-Range Stereodirecting Participation across a Glycosidic Linkage in Glycosylation Reactions.

The formation of an unprecedented 12-membered macrocyclic ketal through the long-range participation of a levulinoyl group across a glycosidic linkage was observed in glycosylation reactions. This finding indicated that stereodirecting participation is not limited to groups within the glycan ring being activated, thus broadening the scope of remote group participation in glycosylation.

Isomer-specific influences on ignition and intermediates of two C5 ketones in an RCM

Ketones have been considered as potential biofuels and main components of blend stock for internal engines. To better understand the chemical kinetics of ketones, ignition delay times of 2-pentanone (propyl methyl ketone, PMK) and 3-pentanone (diethyl ketone, DEK) were measured at temperatures of 895–1128 K under 10 and 20 bar, at equivalence ratios (ϕ) of 0.5 and 1.0 in a rapid compression machine (RCM). To explore the impact of carbonyl functionality and resonance stabilized structures of fuel radicals on their combustion kinetics, high-temperature pyrolysis at 1130 K and relatively low-temperature oxidation at 950 K studies were performed in an RCM, and the time-resolved species concentration profiles under these two conditions were quantified using a fast sampling system and gas chromatography (GC). A new kinetic model containing low-temperature reactions was built aiming at predicting the pyrolysis and oxidation behaviors of both ketones. The consumption pathways of the resonance stabilization fuel radicals through oxygen addition and following reactions are promoted since the decomposition rates of these radicals are about 4 orders magnitudes lower than regular fuel radicals. The occurrences of the so-called “addition-dissociation reactions”, i.e., ketones reacting with a hydrogen yielding aldehyde or reacting with a methyl radical yielding shorter-chain-length ketones, are verified in pyrolysis experiments. Based on experiments and model analysis, the carbonyl functionality in both ketones is preserved during the process of β-scissions of fuel radicals and α-scissions of fuel-related acyl radicals, resulting in the direct formation of CO and ketene. However, the position of carbonyl functionality has a significant impact on the species pools.

Does 'Dry Hit' vaping of vitamin E acetate contribute to EVALI? Simulating toxic ketene formation during e-cigarette use.

Vitamin E acetate (VEA) is strongly linked to the outbreak of electronic-cigarette or vaping product use-associated lung injury (EVALI). It has been proposed that VEA decomposition to ketene–a respiratory poison that damages lungs at low ppm levels–may play a role in EVALI. However, there is no information available on the temperature at which VEA decomposes and how this correlates with the vaping process. We have studied the temperature-dependent kinetics of VEA decomposition using quantum chemical and statistical mechanical modelling techniques, developing a chemical kinetic model of the vaping process. This model predicts that, under typical vaping conditions, the use of VEA contaminated e-cigarette products is unlikely to produce ketene at harmful levels. However, at the high temperatures encountered at low e-cigarette product levels, which produce ‘dry hits’, ketene concentrations are predicted to reach acutely toxic levels in the lungs (as high as 30 ppm). We therefore hypothesize that dry hit vaping of e-cigarette products containing VEA contributes to EVALI.

(2S,3R,6R)-2-[(R)-1-Hydroxyallyl]-4,4-dimethoxy-6-methyltetrahydro-2H-pyran-3-ol

(2S,3R,6R)-2-[(R)-1-Hydroxyallyl]-4,4-dimethoxy-6-methyltetrahydro-2H-pyran-3-ol was isolated in 18% after treating the glucose derived (5R,6S,7R)-5,6,7-tris[(triethylsilyl)oxy]nona-1,8-dien-4-one with (1S)-(+)-10-camphorsulfonic acid (CSA). The one-pot formation of the title compound involved triethylsilyl (TES) removal, alkene isomerization, intramolecular conjugate addition and ketal formation. The compound was characterized by 1H and 13C NMR spectroscopy, ESI mass spectrometry and IR spectroscopy. NMR spectroscopy was used to establish the product structure, including the conformation of its tetrahydropyran ring.

An Experimental and Theoretical Investigation into the Formation of Ketene (H2CCO) and Ethynol (HCCOH) in Interstellar Analog Ices

Abstract The formation of isomers of C2H2O—ketene (H2CCO), ethynol (HCCOH), and oxirene (c-CHCHO)—was investigated in interstellar ice analogs composed of carbon monoxide and water. Using tunable photoionization time-of-flight mass spectrometry to selectively ionize the isomer of interest, ketene and ethynol were detected as reaction products, but oxirene remains elusive. These findings demonstrate that organic compounds that are precursors to complex organic molecules can form without an organic source of carbon. Furthermore, we report the first plausible detection of ethynol in astrophysically relevant ices. These investigations were supported by theoretical calculations describing reaction energies, pathways, ionization energies, and harmonic frequencies.

Role of surface frustrated Lewis pairs on reduced CeO2(110) in direct conversion of syngas

Direct syngas conversion to light olefins on bifunctional oxide-zeolite (OX-ZEO) catalysts is of great interest to both academia and industry, but the role of oxygen vacancy (Vo) in metal oxides and whether the key intermediate in the reaction mechanism is ketene or methanol are still not well-understood. To address these two issues, we carry out a theoretical study of the syngas conversion on the typical reducible metal oxide, CeO2, using density functional theory calculations. Our results demonstrate that by forming frustrated Lewis pairs (FLPs), the VOs in CeO2 play a key role in the activation of H2 and CO. The activation of H2 on FLPs undergoes a heterolytic dissociative pathway with a tiny barrier of 0.01 eV, while CO is activated on FLPs by combining with the basic site (O atom) of FLPs to form CO22−. Four pathways for the conversion of syngas were explored on FLPs, two of which are prone to form ketene and the other two are inclined to produce methanol suggesting a compromise to resolve the debate about the key intermediates (ketene or methanol) in the experiments. Rate constant calculations showed that the route initiating with the coupling of two CO* into OCCO* and ending with the formation of ketene is the dominant pathway, with the neighboring FLPs playing an important role in this pathway. Overall, our study reveals the function of the surface FLPs in the activation of H2 and CO and the reaction mechanism for the production of ketene and methanol for the first time, providing novel insights into syngas conversion over OX-ZEO catalysts.

Theoretical chemical kinetics for catalytic pyrolysis of methyl acetate over H-ZSM-5 zeolites

The catalytic chemistry of methyl acetate (MA) over zeolites was investigated theoretically at the M06-2X/6–311++G(d,p) level, and its chemical reaction rate constants were calculated by using the transition state theory. With particular interest in looking for feasible reactions of the protolytic cracking channels, the present study reveals that the ketene formation in the concerted mechanism and that of acetyloxy + CH3 are competitive reactions during MA consumption. Furthermore, comparisons between the catalytic and conventional pyrolysis of MA were carried out to demonstrate the benefits of introducing the catalysts to MA combustion. It is demonstrated that the energy barriers of the dissociation reactions for MA over H-ZSM-5 zeolites decrease significantly compared with the conventional pyrolysis of MA. Changes of production distributions were also observed between the catalytic pyrolysis and the conventional pyrolysis. The results also provides new insight into the mechanism of the MA catalytic pyrolysis that will guide the improvements in the engine combustion efficiency and in the control of volatile organic compounds, and will also help to improve the selectivity of the conversion of methanol to hydrocarbon and olefin products.

Fischer Carbene Pentannulation with Alkynes Having Adjacent Carbonate or Acyloxy Groups: Synthesis of 3-Substituted 1-Indanones.

Various aryl Fischer carbenes reacted with alkynes having adjacent acyloxy or carbonate groups to regioselectively deliver 3-substituted 1-indanones. The acyloxy or carbonate group probably coordinates with the Cr metal to give a tetra-coordinated chromium complex forming a six-membered ring that retards CO insertion for ketene formation, which is required for benzannulation. Alternatively, the ortho position aryl ring attack results in pentannulation, providing regioselectively 3-substituted 1-indanones. The method is extended to the synthesis of the core structure of 3-epi-mutisianthol.

Oxetan-3-one pyrolysis from the perspective of multireference approaches

The objective of this research is to provide a theoretical explanation of the thermal decomposition of the oxetan-3-one molecule. This process may proceed via at least two distinctive reaction pathways. One of them leads to the formation of ketene and formaldehyde and the other to oxirane and carbon monoxide. We examined, on the basis of multireference approaches, the reaction profiles of oxetan-3-one pyrolysis in terms of Gibb’s free energy. The geometries and thermodynamical parameters of the transition states were obtained and compared to the known experimental facts and calculations. We also show that as some transition states have broken spin-symmetry character in DFT calculations, incorporating multireference approaches seems to be necessary. On the basis of CASPT2 modelling we were able to explain the fundamental experimental finding that the reaction leading to oxirane and carbon monoxide becomes more and more pronounced in higher temperatures and rationalized in terms of entropic contributions.

Infrared spectroscopic detection of ketene formation from carbene and CO sources: an amide synthesis

An effective methodology to detect the highly reactive ketene intermediate, which is formed in situ during the course of organic transformation.

Small-Scale Procedure for Acid-Catalyzed Ketal Formation.

A modified procedure for dehydrative ketal protections is disclosed, which serves as an alternative to the classic Dean-Stark protocol. Studies show that this new procedure can outperform the Dean-Stark apparatus on small scales and thus serves as a complementary approach to effect dehydrative ketalizations. A detailed procedure for this apparatus is presented.

Formation of Acetals and Ketals from Carbonyl Compounds: A New and Highly Efficient Method Inspired by Cationic Palladium

The development of a new, highly efficient, and simple method for masking carbonyl groups as acetals and ketals is described. This methodology relies on the nature of the palladium catalyst to direct the acetalization/ketalization reaction. This new protocol is mild and proceed with a very low catalyst loading at ambient temperatures. The method has been extended to a wide variety of different carbonyl compounds with various steric encumbrances to form the corresponding acetals and ketals in excellent yields.

Addition-Rearrangement of Ketenes with Lithium N- tert-Butanesulfinamides: Enantioselective Synthesis of α,α-Disubstituted α-Hydroxycarboxylic Acid Derivatives.

Addition of the lithium salts of chiral N-substituted tert-butanesulfinamides to ketenes and subsequent silylation initiates stereoselective [2,3]-rearrangement, which affords enantioenriched α,α-disubstituted α-sulfenyloxy carboxamides through a reaction that faithfully transfers the absolute stereochemistry of the lithiated sulfinylamides to the α-carbon of the amide products. This addition-rearrangement can be performed together with ketene formation from acyl chloride in a single flask, providing a new and practical synthetic route to α-hydroxycarboxylic acid derivatives.

Synthesis, characterization and antiproliferative activity of seco analogues of brassinosteroids

Synthesis and structure–activity relationship analysis of a two groups of 2,3-seco analogues of brassinosteroids (BRs) were performed to examine their antiproliferative activities. Two steroid skeletons were chosen for the preparation of seco analogues – cholestane and stigmastane. The synthetic strategy consists of multistep reactions and detailed analysis of compounds prepared. We have discovered unpublished behaviour of 2,3-seco-2,3-dihydroxy-6-ketones leading to formation of intramolecular ketal with two new steroidal rings. Their reaction intermediates were also characterized in some cases. All compounds prepared were fully characterized with NMR and MS techniques. Most of compounds were tested for in vitro cytotoxicity on three cancer cell lines (CEM, MCF7, and HeLa) and normal human fibroblasts (BJ). It was discovered that some seco analogues caused apoptosis in cancer cells. The most promising seco derivative 28 proved to have high therapeutic index.

Inline Reaction Monitoring of Amine-Catalyzed Acetylation of Benzyl Alcohol Using a Microfluidic Stripline Nuclear Magnetic Resonance Setup.

We present an in-depth study of the acetylation of benzyl alcohol in the presence of N,N-diisopropylethylamine (DIPEA) by nuclear magnetic resonance (NMR) monitoring of the reaction from 1.5 s to several minutes. We have adapted the NMR setup to be compatible to microreactor technology, scaling down the typical sample volume of commercial NMR probes (500 μL) to a microfluidic stripline setup with 150 nL detection volume. Inline spectra are obtained to monitor the kinetics and unravel the reaction mechanism of this industrially relevant reaction. The experiments are combined with conventional 2D NMR measurements to identify the reaction products. In addition, we replace DIPEA with triethylamine and pyridine to validate the reaction mechanism for different amine catalysts. In all three acetylation reactions, we find that the acetyl ammonium ion is a key intermediate. The formation of ketene is observed during the first minutes of the reaction when tertiary amines were present. The pyridine-catalyzed reaction proceeds via a different mechanism.